Outliner: Port metaball elements to new tree-element code design

No user visible changes expected.

Part of #96713, continuation of work started in 249e4df110 and 2e221de4ce.
Refer to these for a motivation and design overview.

Adds a new tree-element class for metaball IDs.

Pull Request: https://projects.blender.org/blender/blender/pulls/108654

source/blender/editors/space_outliner/CMakeLists.txt

@@ -60,6 +60,7 @@ set(SRC
   tree/tree_element_id_curve.cc
   tree/tree_element_id_library.cc
   tree/tree_element_id_mesh.cc
+  tree/tree_element_id_metaball.cc
   tree/tree_element_id_scene.cc
   tree/tree_element_label.cc
   tree/tree_element_nla.cc
@@ -82,6 +83,7 @@ set(SRC
   tree/tree_element_id_curve.hh
   tree/tree_element_id_library.hh
   tree/tree_element_id_mesh.hh
+  tree/tree_element_id_metaball.hh
   tree/tree_element_id_scene.hh
   tree/tree_element_label.hh
   tree/tree_element_nla.hh

source/blender/editors/space_outliner/outliner_tree.cc

@@ -553,24 +553,13 @@ static void outliner_add_id_contents(SpaceOutliner *space_outliner,
     case ID_SCE:
     case ID_ME:
     case ID_CU_LEGACY:
+    case ID_MB:
       BLI_assert_msg(0, "ID type expected to be expanded through new tree-element design");
       break;
     case ID_OB: {
       outliner_add_object_contents(space_outliner, te, tselem, (Object *)id);
       break;
     }
-    case ID_MB: {
-      MetaBall *mb = (MetaBall *)id;
-
-      if (outliner_animdata_test(mb->adt)) {
-        outliner_add_element(space_outliner, &te->subtree, mb, te, TSE_ANIM_DATA, 0);
-      }
-
-      for (int a = 0; a < mb->totcol; a++) {
-        outliner_add_element(space_outliner, &te->subtree, mb->mat[a], te, TSE_SOME_ID, a);
-      }
-      break;
-    }
     case ID_MA: {
       Material *ma = (Material *)id;
       if (outliner_animdata_test(ma->adt)) {

source/blender/editors/space_outliner/tree/tree_element_id.cc

@@ -23,6 +23,7 @@
 #include "tree_element_id_curve.hh"
 #include "tree_element_id_library.hh"
 #include "tree_element_id_mesh.hh"
+#include "tree_element_id_metaball.hh"
 #include "tree_element_id_scene.hh"
 
 #include "tree_element_id.hh"
@@ -45,8 +46,9 @@ std::unique_ptr<TreeElementID> TreeElementID::createFromID(TreeElement &legacy_t
       return std::make_unique<TreeElementIDMesh>(legacy_te, (Mesh &)id);
     case ID_CU_LEGACY:
       return std::make_unique<TreeElementIDCurve>(legacy_te, (Curve &)id);
-    case ID_OB:
     case ID_MB:
+      return std::make_unique<TreeElementIDMetaBall>(legacy_te, (MetaBall &)id);
+    case ID_OB:
     case ID_MA:
     case ID_TE:
     case ID_LT:

source/blender/editors/space_outliner/tree/tree_element_id_metaball.cc

@@ -0,0 +1,44 @@
+/* SPDX-FileCopyrightText: 2023 Blender Foundation
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup spoutliner
+ */
+
+#include "DNA_listBase.h"
+#include "DNA_meta_types.h"
+#include "DNA_outliner_types.h"
+
+#include "../outliner_intern.hh"
+
+#include "tree_element_id_metaball.hh"
+
+namespace blender::ed::outliner {
+
+TreeElementIDMetaBall::TreeElementIDMetaBall(TreeElement &legacy_te, MetaBall &metaball)
+    : TreeElementID(legacy_te, metaball.id), metaball_(metaball)
+{
+}
+
+bool TreeElementIDMetaBall::isExpandValid() const
+{
+  return true;
+}
+
+void TreeElementIDMetaBall::expand(SpaceOutliner &space_outliner) const
+{
+  expand_animation_data(space_outliner, metaball_.adt);
+
+  expandMaterials(space_outliner);
+}
+
+void TreeElementIDMetaBall::expandMaterials(SpaceOutliner &space_outliner) const
+{
+  for (int a = 0; a < metaball_.totcol; a++) {
+    outliner_add_element(
+        &space_outliner, &legacy_te_.subtree, metaball_.mat[a], &legacy_te_, TSE_SOME_ID, a);
+  }
+}
+
+}  // namespace blender::ed::outliner

source/blender/editors/space_outliner/tree/tree_element_id_metaball.hh

@@ -0,0 +1,30 @@
+/* SPDX-FileCopyrightText: 2023 Blender Foundation
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup spoutliner
+ */
+
+#pragma once
+
+#include "tree_element_id.hh"
+
+struct MetaBall;
+
+namespace blender::ed::outliner {
+
+class TreeElementIDMetaBall final : public TreeElementID {
+  MetaBall &metaball_;
+
+ public:
+  TreeElementIDMetaBall(TreeElement &legacy_te, MetaBall &metaball);
+
+  void expand(SpaceOutliner &) const override;
+  bool isExpandValid() const override;
+
+ private:
+  void expandMaterials(SpaceOutliner &) const;
+};
+
+}  // namespace blender::ed::outliner